1. Field of the Invention
This invention relates to electric motors and, in particular, to systems for remote transmission of angular position and force between master and slave shafts.
2. Description of the Prior Art
Master-slave manipulators known at present are basically used in extreme conditions dangerous for the operator. It is therefore quite natural that very stringent requirements are set to systems for remote transmission of the angular position and effort from an input shaft to an output shaft which are kinematically connected to respective links of the master-slave manipulator to control the position of its actuators. These requirements include high reliability, durability, and good response to the actions of an operator possessing substantial adaptive capabilities. Specifically, such systems permit static errors in angular position transmission have a comparatively low accuracy in force transmission to the input shaft. These parameters should be within the range of human capabilities. But it should be borne in mind that the load applied to the output shaft may vary over an extremely broad range from practically imperceptible loads to those clearly beyond his physical capabilities. To make the operator-manipulator system serviceable with the load on the output shaft varying over a wide range, the scaling factor of the force transmitted to the input shaft should be variable without interruption of the system operation.
Known in the art is a system for remote transmission of the angular position and force between master and slave shafts, which comprises DC commutator motors kinematically connected with input and output shafts, whose windings are coupled to outputs of amplifiers, motor shaft position sensors connected to inputs of a first comparison element, and torque transducers, one said torque transducer being connected to the input of the second comparison element, while the second torque transducer is connected to the other input of the second comparison element via a converter for proportional signal control, which features a settling input. The output of the second comparison element is connected to the input of the amplifier of the master motor, while the output of the first comparison element is connected to the input of the amplifier of the actuator motor (I. N, Egorov et al., "Proektirovanie slediaschikh sistem dvustoronnego deistviya", 1980, Mashinostroenie Publ, Moscow, pp. 53-58).
In this system the combination of the first comparision element, position sensors, and the actuator motor with the amplifier ensure remote transmission of the angular position, while the second comparison element, torque transducers, and the master motor with the amplifier ensure transmission of power to the input shaft. The operator may change the gain factor of the converter at the setting input thereof when it is required. The converter gain factor is the multiplier for the signal of the load torque transducer. The comparison element generates a signal equal to the difference between the signal corresponding to the torque produced by the operator and the output signal of the converter. The torque developed by the master motor is, therefore, transmitted to the slave shaft as a portion of the load torque assigned by the operator, which corresponds to the change in the scaling factor of the power transmitted to the input shaft.
But the prior art system is deficient in that it makes use of commutator motors which are not reliable and durable since they contain a brush assembly which wears out very fast, particularly in harsh conditions. Torque transducers add to the system unreliability, making it still more complex and prone to faults.
Some of the above disadvantages are eliminated in a system for remote transmission of the angular position and effort between the input and output shafts, which comprises master and slave synchronous motors kinematically connected to input and output shafts, shaft position sensors whose outputs are connected to inputs of a comparison element having its input connected to a control input of a unit for generating current in windings of the synchronous motors. Respective windings of the synchronous motors are connected to each other and connected to outputs of the current generating unit. The output of the shaft position sensor of the slave synchronous motor is connected to the setting input of the unit for generating current in the windings of the master and slave synchronous motors (SU, A, 1176425).
This system is much more reliable and durable as compared to the one described above due to the use of synchronous motors having no brush-commutator units and capable of withstanding much more severe conditions. The absence of torque transducers also adds to the system reliability. But this system is deficient in that the scale factor of the force transmitted to the master shaft depends on the load and the operator has difficult time estimating the efforts applied to the actuator shaft. Moreover, the operator cannot adjust the scale factor while the system is operating, which is a serious restriction to varying the slave shaft load.
Also known in the art is a system for remote transmission of the angular position and force between master and slave shafts (SU, A, 1257690), which comprises master and slave synchronous motors whose shafts are connected, respectively, to master and slave shafts and provided with position sensors electrically connected to inputs for setting the orientation of magnetic fields of stators of the master and slave synchronous motors and to information inputs of a device for setting the amplitude of the magnetic fields of the stators of the master and slave synchronous motors, the output of the amplitude setting device being electrically connected to a control input of a unit for generating current in the windings of the master and slave synchronous motors, the setting input of said current generating unit being connected to the output of the unit for setting orientation of the magnetic fields of the master and slave synchronous motors, while the inputs thereof are connected to electrically connected respective windings of the master and slave synchronous motors.
In this system, the device for setting the amplitude of the stator magnetic fields is built around a comparison element. The unit for assigning the orientation of the stator magnetic fields comprises an adder whose inputs are inputs of the orientation assigning unit, while the output of the adder is connected to the input of a divide-by-two circuit whose output is the output of the orientation assigning unit.
This system is designed so that the scale factor of forces transmitted to the master shaft remains unchanged during the operational cycle. In this way the range of load variation on the slave shaft is made somewhat wider as compared to the system where the scale factor changes with the load. But the available load variation range on the slave shaft is still not sufficient for this system to be used in master-slave manipulators designed for operation in extreme conditions. In addition, the mismatch of the shafts of the master and actuator motors still depends on the torques produced by the operator and the load, which affects the accuracy of the shaft angular position transmission.